1. Field of the Invention
The present invention relates generally to an optical distance measuring apparatus operable in accordance with a phase difference detecting process. More particularly, the present invention relates to an optical distance measuring apparatus of the aforementioned type wherein a distance between the apparatus and an object to be measured can optically be determined with a high accuracy. Further, the present invention relates to an optical distance measuring apparatus operable in accordance with a time difference detecting process.
2. DESCRIPTION OF THE PRIOR ART
To facilitate understanding of the present invention, a typical conventional optical distance measuring apparatus operable in accordance with a phase difference detecting process will briefly be described below with reference to FIG. 3.
FIG. 3 is a block diagram of the conventional optical distance measuring apparatus operable in accordance with a phase difference detecting process, particularly illustrates the whole structure of the apparatus. The apparatus includes a reference oscillating circuit 1 from which a reference signal is output to a light emitting element 3 via a buffer gate circuit 2 in the form of an optical signal. Subsequently, as the light emitting element 3 is activated in response to the reference signal output from the reference oscillating circuit 1, a distance measuring light beam L.sub.1 is emitted toward an object P to be measured through an optical lens system (not shown).
Thereafter, the distance measuring light beam L.sub.1 is reflected from the object P in the form of a reflected light beam L.sub.2 which in turn is received by a light receiving element 4. After the receipt of the reflected light beam L.sub.2, an output derived from the reflected light beam L.sub.2 is input into an alternate current amplifier 6 via an automatic gain controlling amplifier 5, and the amplified output signal is then input into a digital type mix-down circuit 8 via a wave form correcting circuit 7.
The mix-down circuit 8 is adapted to operate to reduce the frequency of each signal based on a phase difference between the electrical phase of the reference signal output from the reference oscillating circuit 1 and the electrical phase of a local oscillation signal output from a local oscillator 9 without any variation of these electrical phases. Subsequently, an output generated from the reference oscillating circuit 1 in the form of a reference signal and an output derived from the reflected light beam L.sub.2 received by the light receiving element 4 are input into a central processing unit 10 which in turn determines a distance between the apparatus and the object P by measuring the phase difference between the electrical phase of the reference signal and the electrical phase of the amplified signal derived from the reflected light beam L.sub.2 transmitted from the light receiving element 4.
It should be noted that in view of the fact that an optical lens system (not shown) employable for the conventional optical measuring apparatus is well known by one expert in the art, a detailed description on the optical lens system is omitted for the purpose of simplification.
However, it has been found with respect to the conventional optical distance measuring apparatus constructed as described above that a large volume of phase correction data is required because a phase delay varies dependent on the extent of amplification in the automatic gain controlling amplifier 5, which in turn causes the phase error associated with the resultant gain to be incorrectly compensated. Thus, the distance between the apparatus and the object to be measured can not be determined with high accuracy.
The present invention has been made with the foregoing background in mind.
An object of the present invention is to provide an optical distance measuring apparatus operable in accordance with a phase difference detecting process wherein a phase error associated with a gain can correctly be compensated so as to determine a distance between the apparatus and an object to be measured.
Other object of the present invention is to provide an optical distance measuring apparatus of the aforementioned type which assures that a distance measuring operation can be performed with a high accuracy.
Another object of the present invention relates to an optical distance measuring apparatus operable in accordance with a time difference detecting process wherein a distance between the apparatus and an object to be measured can be determined based on a time difference between the time when a signal output from a light receiving portion in response to receipt of a reflected light beam is input into a central processing unit and the time when a reference signal output from a reference oscillator is input into the central processing unit.
According to one aspect of the present invention, there is provided an optical distance measuring apparatus operable in accordance with a phase difference detecting process, wherein the apparatus comprises a light emitting portion including a light emitting element and a light source from which a distance measuring light beam is emitted toward an object to be measured; an optical lens system for allowing the distance measuring light beam to be oriented to the distant object whose distance is to be measured from which the distance measuring light beam is reflected in the form of a reflected light beam; a light receiving portion including a light receiving element for receiving a reflected light beam reflected from the object whose distance is to be measured through the optical lens system; and a processing system comprising a first circuit system on the light emitting side and a second circuit system on the light receiving side and including a central processing unit and a digital type mix-down circuit for detecting and calculating a phase difference between the electrical phase of a signal derived from the reflected light beam and the electrical phase of a reference signal output from a reference oscillator electrically connected to the light emitting portion via a buffer gate circuit so as to determine a distance between the apparatus and the object to be measured with reference to the electrical phase of a local oscillation signal output from a local oscillator.
In addition, according to other aspect of the present invention, there is provided an optical distance measuring apparatus operable in accordance with a time difference detecting process, wherein the apparatus comprises a light emitting portion including a light emitting element and a light source from which a distance measuring light beam is emitted toward an distant object spaced at a distance to be measured; an optical lens system for allowing the distance measuring light beam to be oriented to the object to be measured from which the distance measuring light beam is reflected in the form of a reflected light beam; a light receiving portion including a light receiving element for receiving a reflected light beam reflected from the object whose distance is to be measured through the optical lens system; and a processing system comprising a first circuit system on the light emitting side and a second circuit system on the light receiving side and including a central processing unit and a digital type mix-down circuit for detecting and calculating a time difference between the time when a signal output from the light receiving portion in response to receipt of the reflected light beam is input into the central processing unit and the time when a reference signal output from a reference oscillator electrically connected to the light emitting portion via a buffer gate circuit is input into the central processing unit so as to determine a distance between the apparatus and the object whose distance is to be measured with reference to the time when a local oscillation signal output from a local oscillator is input into the central processing unit.
The first circuit system on the light emitting side includes a modulating circuit electrically connected to the light emitting portion and a buffer gate circuit electrically connected to the reference oscillator.
On the other hand, the second circuit system on the light receiving side includes a demodulating circuit electrically connected to the light receiving portion, a ladder resistance type attenuation circuit, a multiplexer, an alternating current amplifier, a wave shape correcting circuit electrically connected to the central processing unit via the mix-down circuit and a signal amplitude detecting circuit having an input side electrically connected to the alternating current amplifier and an output side electrically connected to the central processing unit.
The attenuation circuit includes connection points at respective ladder portions, and one of the connection points is changeably selected by the central processing unit so as to allow the selected connection point in the attenuation circuit to be electrically connected to the corresponding channel in the multiplexer, whereby the signal derived from the reflected light beam is input into the mix-down circuit via the alternating current amplifier and the wave shape correcting circuit.
When the signal amplitude detecting circuit detects that the signal derived from the reflected light beam has an amplitude in excess of a predetermined value, the central processing unit changeably controls the multiplexer so as to reduce a magnitude of the amplitude of the signal.
In addition, the central processing unit contains data on phase correction corresponding to a channel in the multiplexer through which the signal derived from the reflected light beam passes, so as to correct data regarding the measured distance with reference to data on phase correction.
Additionally, the attenuation circuit includes a plurality of channels one of which is taken as a reference channel. To assure that a distance measuring operation is performed with a high accuracy, data representing an error appearing between adjacent channels associated with the reference channel is memorized in a memory of the central processing unit so as to properly compensate an error when the latter actually appears therebetween.
Other objects, features and advantages of the present invention will readily become apparent from a reading of the following description which has been made in conjunction with the accompanying drawings.